1. Field of the Invention
The present invention relates to construction and design of microwave multiplexers which may or may not have contiguous channels. In these devices, a broadband input microwave signal, through filtering techniques, is divided into a number of different narrower-bandwidth output signal components. The most challenging designs involve situations where the passbands of the output channels are contiguous, accommodating the entire input frequency band.
The design of microwave multiplexer circuits can present a particular challenge, especially if low transmission losses and high channel selectivities are to be achieved in conjunction with contiguous channel operation. These combined requirements inherently translate into significant interdependencies among individual frequency-selective segments of the multiplexer, which may result in having to account for an inconveniently large number of circuit variables simultaneously.
2. The Prior Art
The prior art in the field of antenna design has utilized log-periodic principles. These principles have, however, not been successfully applied to the design of microwave multiplexers. An article entitled "Log-Periodic Transmission Line Circuits--Part 1: One-Port Circuits," R. H. DuHamel and M. E. Armstrong published in IEEE Transactions on Microwave Theory and Techniques, Volume MTT-14, No. 6, June 1966, describes the use of log-periodic scaling in transmission line circuits. The DuHamel and Armstrong article is hereby incorporated by reference and made a part of applicant's disclosure.
The DuHamel article discloses a theoretical study of one-port log-periodic circuits consisting of a transmission line shunt-loaded with open-circuit transmission line stubs. The article suggests the possibility of multiport circuits, but does not provide any information or disclosure which would enable one to design such a multiport circuit. The author titled the reference article as "Part I." However, there has never been a publication of a second or further part which would describe circuits other than one-port circuits. Therefore, the literature is devoid of any disclosure of design techniques wherein log-periodic transmission line multiport circuits are disclosed. The DuHamel article at page 271 refers to PART II--Two-Port Circuits. This article, however, never materialized. Therefore, the prior art has recognized that a multiport log-period transmission line device can be built, and may be desirable. However, the art has never taught those working in the art how to achieve an operable log-periodic multiport circuit that can fulfill a practical need.